Prior art ultrasound imaging is essentially black-and-white: The ultrasonic medical color imaging currently available on market is actually the combination of a black-and-white ultrasound reflection image and a Doppler blood flow image using red and blue color to indicate blood flows moving in the opposite directions within blood vessels. U.S. Pat. No. 6,579,240 further expanded color-coded moving objects to solid structures such as pumping cardiac walls. Technically, with the exceptions of cardiac moving structures and blood flow, medical ultrasonic imaging is still in the age of black-and-white, or the age of B-mode (Brightness-mode). Industrial ultrasonic inspection is far more behind in terms of utilizing images.
Pseudo-color image: There is another type of commercially available medical ultrasonic imaging with color display—medical images are expressed in brightness of a soft color such as orange-gray, green-gray, instead of black-and-white. These color images carry no more information than their black-and-white counterpart, are no comparison with color photos or color TV pictures in terms of information richness associated with color. Moreover, color ultrasound imaging has been widely used to refer to ultrasonic imaging device with Doppler blood flow functionality, leaving a not-so-desirable name—“pseudo-color” for brightness color imaging.
Topographic color image: There is yet another type of ultrasonic color image with a coloring method borrowed from topography. Topographic maps published all over the world use colors to express different altitudes: dark blue for deep oceans of lowest altitude, light blue for shallow oceans, green for plains, dark brown for plateaus with highest altitudes, etc. Using brightness in the place of altitude in topographic, a black-and-white ultrasound image becomes a color image. However, topographic color images are never popular, because it provides no more information and no improvements in image reading and abnormality discrimination. It is fair to say that ultrasonic image with topographic coloring is even more pseudo.
The role of color in ultrasound imaging: The ultrasound signals retrieved by an ultrasonic probe do carry information about the interior distributions of acoustic properties of the target, but carry essentially nothing about visual properties such as color. The coloring of prior art ultrasonic imaging, may it be the brightness of grey or other soft colors, topographic coloring, or red-and-blue of Doppler blood flows, is unrelated to the actual color of human organ or tissues. Any color similarities are either accidental or artificial assignment, have nothing to do with the sciences and technologies behind ultrasonic imaging. Both the medical professionals who perform and the patients who receive ultrasound imaging are aware of that the coloring of the images is not real. In facts, not relating to the actual color of target is an advantage rather than a weakness. When something abnormal has happened to a human organ, the color deviations may not be noticeable, but changes in tissue density and elasticity can affect the local acoustic characteristics. The capability of detecting and showing such acoustic deviations is an invaluable advantage of ultrasonic imaging over visual and optical examinations (such as endoscope). Clearly, showing the true color of target should not be a goal pursued by ultrasonic imaging.
Two reasons of using image: There are two primary reasons why ultrasonic medical diagnoses convert non-visual information into visible images. The first reason is space perceiving capability of human visual sense. Human's space perception is a natural instinct requiring no training. An image may not tells desired physical properties of the target, but it always shows the spatial properties such as the locations, shapes, sizes, relative positioning with surrounding objects, etc. The second and more important reason is the extraordinary efficiency that human visual sense possesses when picking up external information. The amount of information that a human brain gets via a glimpse, takes years of listening if converted into audio information to play out without interruption. In technology language, visual sense has a bandwidth substantially greater than that of hearing sense or any other human senses. Because of the excellent spatial perception and tremendous bandwidth of human vision, modern medical diagnosis technologies, such as ultrasound, magnetic resonance, X-ray, CT, all choose image as the primary way for presenting information obtained via all kinds of physical means.
Color means bandwidth: Color has very little to do with spatial perception, but fundamentally impacts the bandwidth For a commonly seen 7 bit brightness image, each image point can be expressed in one of 128 possible brightness levels. In comparison, in a common 7 bit color image, each image point is expressed by three 7 bit color parameters, each can independently take one of 128 possible values, providing 2,097,152 (the cube of 128) possible color alternatives for each image point. In general, the information carried by a color image is the cube of information carried by a brightness image. Because of human vision's born capability of perceiving color, the bandwidth of human vision reading a color image is the cube of the bandwidth of reading a brightness image. It is a pity that existing medical imaging methods, including ultrasound, only utilize a tiny fraction of the bandwidth of human vision. This is exactly what present invention aimed to change.
Another limitation of prior art: Ultrasound can penetrate into non-transparent objects, generating sectional profiles of target without actually cutting through the target. Traditional ultrasonic imaging uses only a single parameter, most often the reflection coefficient of ultrasound signal at image point, to produce an image. Since sound reflection only takes place on an interface between two different materials, such as the contour surface separating a human organ from surrounding tissues, the boundaries of cracks, bubbles or impurities in a machine part, typical ultrasound profile image, such as B-mode ultrasound medical image, is composed of contour lines of different brightness representing exterior and interior interfaces of the target. In order to show interfaces within the target, the sole imaging parameter is reserved to quantify reflection characteristics, leaving single parameter based prior art imaging no effective way of expressing continuous acoustic medium bodies enclosed within the structure boundaries.